1. Field of the Invention
The present invention relates to an optical receiver and, in particular, to an optical receiver with a threshold voltage convergence and audio apparatus and communication apparatus using the optical receiver.
2. Description of the Related Art
With the advance of ubiquitous communications, the home network system, which has been limited to sharing printer and Internet connections, is developed to the multimedia home network system internetworking various electric appliances such as TV, audio system, and video system in real time.
Such a home network system is implemented by connecting the electric appliances through one or more wired and wireless networks. The optical link is the most appropriate link for implementing IEEE 1394 network for home, media oriented system transport (MOST) network for automobiles, and office network since it is lighter than electric wire in weight while guaranteeing high data rate with low data loss.
In order to apply the optical link to mobile devices such as cellular phone and MP3 player, the light weight and thin profiles of their internal elements are the design focus together with low power consumption. Until now, however, most of the optical transmitters and receivers are fabricated through bipolar junction transistor (BJT) process such that the devices are large in size relative to when fabricated using complementary metal oxide semiconductor (CMOS) technique, resulting in relatively high power consumption. Also, such conventional optical transmitters and receivers do not satisfy the data rate requirement of high performance audio standards such as DVD-Audio (96 KHz, 24 bits multichannel) and SACD (2822.4 kHz, 1 bit, Multichannel).
Typically, digital audio devices and other industrial devices require optical receiver that can recover digital input signals in wide dynamic range as well as both DC (continuous 0 and 1) and AC data.
The CMOS optical receiver can be implemented with an Automatic Gain Control (AGC) or Automatic Threshold Control (ATC) according to the kinds of control signals. Typically, the AGC-based optical receiver requires high speed devices for securing stability and accuracy of feedback system and an offset removal technique that increase the manufacturing costs and system complexity.
Meanwhile, the ATC-based optical receiver can be implemented in low manufacturing cost with a feed-forward system using low speed devices relative to the AGC-based optical receiver. However, recent ATC technique adopts a DC offset removal method for generating an accurate threshold voltage and a reset circuit for adjusting the threshold voltage in accordance with varying received power, as in the AGC technique, resulting in increase of complexity.
FIG. 1 is a block diagram illustrating a configuration of a conventional CMOS optical receiver, which includes an optical detector, a transimpedance amplifier (TIA), an ATC circuit, and a comparator. The ATI converts the current signal generated by the optical detector into amplified voltage signal, and the ATC circuit generates a threshold voltage in proportion to the received power. The voltage signals generated by the respective TIA and ATC are provided to the comparator so as to be converted into a digital signal of a logic level.
The optical detector and TIA can generate various levels of current and voltage signals according to the length of the optical fiber and variation of the received power such that the recovering such signals with a fixed threshold voltage causes a pulse-width distortion, resulting in quality deterioration of digital audio signal. In order to overcome this problem, the ATC circuit detects two peak signals output from the TIA and outputs an average voltage of the two peak signals.
However, such ATC circuit generates DC-offset by the false settings of the peak detector and resisters. In order to compensate the DC-offset, an offset removal circuit is required. Also, the ATC circuit requires additional reset circuit for generating, when the received power varies, an accurate threshold voltage by discharging capacitor of the peak detector before the varied signal is input. These offset-removal and reset circuits increase the system complexity.
As described above, the conventional optical receiver is disadvantageous in system complexity and manufacturing cost with the requirement of the offset-removal and reset circuits.